1. Field of the Invention
This invention relates generally to ground proximity warning systems, and more particularly to a system that provides a warning to the pilot of a rotary wing aircraft, such as a helicopter, if the descent rate of the aircraft is excessive for the altitude at which the aircraft is flying. Such a warning is particularly useful during approach and landing phases of aircraft operation.
2. Description of the Prior Art
Systems for providing the pilot of an aircraft with a warning in the event that the aircraft is descending too rapidly, particularly on approach to a landing, are known. Examples of such systems are disclosed in U.S. Pat. Nos. 3,946,358; 3,947,808; 3,958,219 and 4,215,334, all assigned to the same assignee as the assignee of the present invention.
While all of the above systems serve the basic function of alerting the pilot if the descent rate of the aircraft exceeds a predetermined safe rate determined by the altitude above ground of the aircraft, the above described systems are designed to operate with transport aircraft, particularly with large, turbine-powered aircraft of the type flown by commercial airlines. However, since rotary wing aircraft are substantially more maneuverable than transport aircraft, systems designed for transport aircraft tend to provide false or nuisance warnings when no unsafe condition exists. Consequently, pilots tend to ignore the warnings provided by such systems, and the system becomes ineffective.
One system designed specifically for helicopters is described in U.S. Pat. No. 4,293,840. This system monitors the descent rate of the aircraft, as determined by the radio altitude rate, and generates a warning if the descent rate is excessive for the altitude at which the aircraft is flying. However, even though this system is much more suitable for use in rotary wing aircraft than is a system designed for transport aircraft, the system described in the '840 reference is a relatively complex system that adjusts the altitude at which the warning is generated as a function of the forward speed of the aircraft. Also, the system disclosed in the '840 reference appears to be designed for use in non-tactical aircraft operation, and consequently it will have a tendency to generate false warnings when used in an aircraft engaged in tactical maneuvers.